The present invention is directed to new and useful improvements in nozzles of the type used to mix gas with a fluid stream for the purpose of generating a stream of foam. More particularly, the invention is directed to a nozzle having an impingement pin therein adapted to facilitate a thorough mixing of gas with a liquid foam producing agent.
Foams are typically produced by the mixing under proper conditions of a chemical, water and a gas. The particular chemicals used depends upon the use to which the foam will be put, which uses can be widely varied. In the agricultural field, foams are often used as pesticides, and are usually preferable to liquids used for this purpose because of ameliorated wind dispersion problems, and reduced run-off and evaporation once on the vegetation. Because foam is readily visible, it also provides a convenient method of visually determining spray coverage. Foams are also widely used for cleaning operations, whether for articles of living areas. One particularly popular use is in connection with floor coverings such as carpets and rugs. A third important use for foam is in connection with fire fighting equipment. Such equipment may be fixed and automatic, or mobile and manually-operated. For each of these uses it is of great importance that the foam be of substantially uniform consistency and that it be distributed evenly wherever it is applied.
In general, two basic methods have been utilized to generate such foams. One method is through the use of a chemical foaming agent which is added to the solution to be sprayed. The other method is by the introduction of gas such as air into the liquid to form minute bubbles, thereby forming the foam. This latter method is the one to which the present invention relates.
The introduction of air bubbles into a liquid is often done through the use of air aspirating nozzles. In such nozzles, a liquid foam producing agent is introduced into one end of the nozzle and, through the use of one or more orifices, is formed into one or more high velocity streams. Each of these streams is directed past air inlet apertures in the sides of the nozzle, thereby causing air to be aspirated into the nozzle by the resulting reduction in pressure within the nozzle. The flow of the stream is then disrupted to facilitate the mixing of the air and the foam producing agent. This is often done through the use of one or more mesh screens. One such nozzle is disclosed in U.S. Pat. No. 3,784,111. Another means for disrupting the stream flow is through the use of impingement surfaces. For example, U.S. Pat. No. 3,836,076 discloses a nozzle with an inclined annular surface formed on the inner periphery of the nozzle body. This surface is designed to deflect the stream inward to mix the foam producing agent with the gas which is present within the nozzle. A second embodiment of this patent uses a circular impingement disc to disrupt the flow and thereby generate foam.
Each of the above-described nozzles includes a slotted outlet designed to produce a flat, fan-shaped spray of foam. However, despite these attempts to fully mix the foam producing agent with air, these prior designs have been unable to perform in a superior fashion for the applications discussed above. Moreover, the means for disrupting the stream flow in conventional nozzles is not adequately complemented with the slotted outlet to provide a wide, uniform, flat spray of foam.
A German Pat. No. 884,912 to Arentoft discloses the use of a vibrating plate positioned within the axial path of the fluid which is passing through the valve wherein the vibration in the plate is induced by impingement of the fluid on the plate. This design is similarly inadequate in generating foam because, among other reasons, Arentoff has not even attempted to complement the impingement means with a slotted outlet.
The present invention responds to the problems presented in the prior art by providing a superior nozzle and method for generating foam which includes a nozzle body, a nozzle inlet, orifice means, gas inlet means, pin means and a nozzle outlet. The nozzle body has upstream and downstream ends and an inner wall defining a passage within the nozzle body. The nozzle inlet at the upstream end of the nozzle body permits introduction of a liquid foam producing agent into the passage. The foam producing agent then passes through the orifice means, thereby forming a stream. This stream is directed past the gas inlet means in the nozzle body, thus reducing the pressure in the passage and causing gas at atmospheric pressure to be aspirated into the passage. The stream is then impinged against the pin means disposed transversely across the passage. At least the upstream half of the cross-section of the pin means is annular so that the pin means disrupts the flow of the stream and splits it into secondary streams. These secondary streams are directed outwardly, passing to each side of the pin means and diverging with respect to each other prior to being deflected inwardly off the inner wall of the nozzle body. The nozzle outlet comprises a transverse slot disposed parallel to the pin means so that a thorough mixing between the gas and foam producing agent is effected prior to discharge through the nozzle outlet as foam.
These and other objects, features and advantages of the present invention will be apparent from the following description, appended claims and annexed drawings.